This description relates to spectrally adjustable filtering.
Devices that spectrally filter and/or detect light can be used in optical communication systems, such as wavelength division multiplexed (WDM) systems, for adjustable filtering and attenuation of spectral components (or “wavelengths” or “channels”) that are multiplexed together in the WDM spectrum. Such devices can be used for optical detection and monitoring of spectral components in the WDM spectrum. Typically, each spectral component has a nominal wavelength corresponding to the center frequency of a channel. In some systems, each spectral component has a spectral shape with a central lobe that has a narrow enough linewidth such that adjacent spectral components, whose center frequencies are separated by a given channel spacing, do not overlap significantly. In some systems, spectral components comprise respective sub-bands of wavelengths over a continuous spectrum that does not necessarily have any separation between adjacent spectral components. It is understood that the term “spectral component” as used herein should be construed broadly, and encompasses these various examples.
Wavelength filtering devices are typically classified as fixed or adjustable. Fixed devices filter a predetermined spectral band while adjustable filters allow reconfiguration of the wavelengths being filtered. Adjustable filtering devices provide the ability to dynamically update system configuration to optimize parameters such as transmission performance and bandwidth utilization. Adjustable filters also enable system operators to provision (turn up) new wavelengths and services.
Optical spectrum monitoring devices can be used within a WDM system to monitor system performance by measuring one or more optical signal attributes including wavelength, optical power, optical signal-to-noise ratio (OSNR), spectral shape, bit-rate, and polarization state, among others. The information provided by optical spectrum monitors may be utilized for system health reporting, fault location and analysis, feedback control and system optimization, and for other purposes.